1. Field of the Invention
This invention relates to polyester multifilament yarn with high modulus and low shrinkage particularly useful for the textile reinforcement of tires. The yarn of the invention provides high treated cord tenacity while maintaining or increasing treated cord dimensional stability when compared to prior art yarns. A process for production of the multifilament polyester yarn is an aspect of the invention.
2. Description of the Prior Art
Polyethylene terephthalate filaments of high strength are well known in the art and are commonly utilized in industrial applications including tire cord for rubber reinforcement, conveyor belts, seat belts, V-belts and hosing.
Continued improvement in high strength industrial yarns particularly suited for use as fibrous reinforcement in rubber tires is an ongoing need in the industry. In particular, the improvement of treated cord tenacity and dimensional stability are desired objectives. U.S. Pat. No. 4,101,525 to Davis et al. provides an industrial strength multifilament polyester yarn with high initial modulus and low shrinkage. Although Davis et al. does not provide treated cord data, it is commonly known that compared to conventional tire cords such yarn provides a reduced tenacity when the yarn is converted to the treated tire cord. Additionally, rapid cooling of the filament immediately after emerging from the spinneret can result in excessive filament breakage and thus yield yarn with poor mechanical quality. U.S. Pat. No. 4,491,657 to Saito et al. discloses high modulus, low shrinkage polyester yarn, but requires a low terminal modulus to achieve good yarn to treated cord conversion efficiency for such dimensionally stable yarns. The low terminal modulus is carried over into the treated cord and results in a lower tenacity than the high terminal modulus cords of the present invention. Also, as shown in FIG. 8, the process of Saito et al. requires highs spinning speeds, which makes it difficult to process on-panel, i.e. a continuous spin-draw process.
The subject matter herein is directed to a process for the production of a drawn polyethylene terephthalate yarn which translates to a high tenacity dimensionally stable tire cord. The process comprises (a) extruding a molten melt-spinnable polyethylene terephthalate having an intrinsic viscosity of at least about 0.8 through a shaped extrusion orifice having a plurality of openings to form a molten spun yarn; (b) solidifying gradually said molten spun yarn by passing said molten spun yarn through a solidification zone which comprises (i) a retarded cooling zone and (ii) a cooling zone adjacent said retarded cooling zone where, in said cooling zone, said yarn is rapidly cooled and solidified in a gaseous atmosphere; (c) withdrawing at sufficient speed said solidified yarn from said solidification zone to form a crystalline partially oriented yarn; and (d) hot drawing said crystalline partially oriented yarn at a total draw ratio between about 1.5/1 and about 2.5/1 to produce a drawn yam having an effective crosslink density (N) between about 10xc3x971021 and about 20xc3x971021 crosslinks per cubic centimeter.
The subject matter herein further is directed to spun polyester fiber having crystallinity of about 3 to about 15 percent and melting point elevation of about 20xc2x0 C. to about 10xc2x0 C.
The subject matter herein further is directed to a drawn polyester yarn having the following properties: tenacity of at least about 7 grams per denier; an amorphous orientation function of less than about 0.75; dimensional stability defined by E4.5=FS less than 13.5 percent; and an effective crosslink density (N) between 10xc3x971021 and 20xc3x971021 centimeters per cubic centimeter.